This invention relates to the processing of finely divided carbonaceous materials to permit the recovery of a solid product. Typically, coal or other carbonaceous material is ground to fine particle size (less than 0.6 mm) prior to the removal of ash and sulfur containing minerals in processes such as cycloning and froth floatation. The resulting slurry is most economically dewatered by mechanical means but mechanical dewatering becomes less effective for ultrafine coal particles because of the high surface area.
Recent developments in coal cleaning require ultrafine particle size to take advantage of the increased liberation of mineral matter and pyrite. These processes produce ultrafine clean coal which is extremely difficult to dewater adequately. Consequently, difficult problems involving increased shipping costs, unwanted moisture, freezing and dilution of BTU content remain to be addressed.
Although thermal drying is an effective method of moisture reduction in finely divided materials, high energy costs may make it infeasible or uneconomical. In addition, a completely dried, finely divided product can introduce environmental problems in handling, transportation and storage including dust pollution, spontaneous combustion explosion and wind erosion.
One attempt to address these problems involves reconstitution of the finely divided carbonaceous material by pelletizing, briquetting or compaction. Representative techniques are disclosed in the assignee's commonly owned U.S. Pat. No. 4,615,712 to Wen.
Therefore, in view of the above, it is one object of the present invention to provide an improved process for the dewatering and reconstitution of finely divided carbonaceous material.
It is a further object of the present invention to provide a process for reconstituting carbonaceous material wherein dust emissions during transportation, handling and storage are ameliorated.
It is also an object of this invention to combine the dewatering, reconstitution and hardening of finely divided carbonaceous materials.
It is likewise an object to provide a process for producing dustless consolidated clumps of finely divided coal particles.